The Microfluidic Ice Nuclei Counter Zürich (MINCZ): a platform for homogeneous and heterogeneous ice nucleation

[摘要] Ice nucleation in the atmosphere is the precursor toimportant processes that determine cloud properties and lifetime.Computational models that are used to predict weather and project futureclimate changes require parameterizations of both homogeneous nucleation(i.e. in pure water) and heterogeneous nucleation (i.e. catalysed byice-nucleating particles, INPs). Microfluidic systems have gained momentumas a tool for obtaining such parameterizations and gaining insight into thestochastic and deterministic contributions to ice nucleation. To overcomethe shortcomings of polydimethylsiloxane (PDMS) microfluidic devices withregard to temperature uncertainty and droplet instability due to continuouswater adsorption by PDMS, we have developed a new instrument: theMicrofluidic Ice Nuclei Counter Zürich (MINCZ). In MINCZ, droplets witha diameter of 75  µm are generated using a PDMS chip, and hundreds of these droplets are then stored in fluoropolymer tubing that is relativelyimpermeable to water and solvents. Droplets within the tubing are cooled inan ethanol bath. We validate MINCZ by measuring the homogeneous freezingtemperatures of water droplets and the heterogeneous freezing temperaturesof aqueous suspensions containing microcline, a common and effective INP inthe atmosphere. We obtain results with a high accuracy of 0.2 K in measured droplet temperature. Pure water droplets with a diameter of 75  µm freeze at a median temperature of 237.3 K with a standard deviation of 0.1 K. Additionally, we perform several freeze–thaw cycles. In the future, MINCZ will be used to investigate the freezing behaviour of INPs, motivated by a need for better-constrained parameterizations of ice nucleation in weather and climate models, wherein the presence or absence of ice influences cloud optical properties and precipitation formation.

[学科分类] 内科医学